> 20 марта 2021 г., в 00:35, Mark Dilger <mark.dil...@enterprisedb.com> > написал(а): > > > >> On Jan 21, 2021, at 6:48 PM, Justin Pryzby <pry...@telsasoft.com> wrote: >> >> @cfbot: rebased >> <0001-Reorganize-pglz-compression-code.patch> > > Review comments.
Thanks for the review, Mark!
And sorry for such a long delay, I've been trying to figure out a way to do
things less-platform dependent.
And here's what I've come up with.
We use pglz_read32() not the way xxhash and lz4 does - we really do not need to
get 4-byte value, we only need to compare 4 bytes at once.
So, essentially, we need to compare two implementation of 4-byte comparison
bool
cpm_a(const void *ptr1, const void *ptr2)
{
return *(const uint32_t *) ptr1 == *(const uint32_t *) ptr2;
}
bool
cmp_b(const void *ptr1, const void *ptr2)
{
return memcmp(ptr1, ptr2, 4) == 0;
}
Variant B is more portable. Inspecting it Godblot's compiler explorer I've
found out that for GCC 7.1+ it generates assembly without memcmp() call. For
x86-64 and ARM64 assembly of cmp_b is identical to cmp_a.
So I think maybe we could just stick with version cmp_b instead of optimising
for ARM6 and similar architectures like Arduino.
I've benchmarked the patch with "REINDEX table pgbench_accounts" on pgbench -i
of scale 100. wal_compression was on, other settings were default.
Without patch it takes ~11055.077 ms on my machine, with patch it takes
~9512.411 ms, 14% speedup overall.
PFA v5.
Thanks!
Best regards, Andrey Borodin.
v5-0001-Reorganize-pglz-compression-code.patch
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